1. Field of the Invention
The present invention relates to a dry etching apparatus used in the manufacture of semiconductor devices, and more particularly, to a two parallel plate electrode type dry etching apparatus using microwaves.
2. Description of the Related Art
A dry (plasma) etching apparatus has been broadly used in obtaining a fine structure of semiconductor devices. Particularly, when use is made of microwaves, the isotropic etching characteristic is excellent, the energy of ions can be arbitrarily controlled, and a fine structure having a large aspect ratio can be obtained.
In a prior art dry etching apparatus (see: JP-A-SHO56-155535), microwaves generated in a microwave oscillator are supplied along a waveguide through a microwave introduction window into a plasma generating chamber, to thereby excite plasma. Then, the excited plasma is supplied from the plasma generating chamber via a plasma intake window into a substrate processing chamber, to thereby etch a semiconductor substrate. This will be explained in detail later.
In the above-mentioned prior art dry etching apparatus, however, since a region where the excited plasma is uniform is limited by the size of the microwave introduction window and the size of the plasma intake window, the etching rate is not uniform, particularly in a large size semiconductor substrate such as an 8 inch (20.3 cm) wafer.
In order to make the etching rate for a large size semiconductor substrate uniform, one suggested approach may be to enlarge the microwave introduction window as well as the plasma intake window; however, this approach is actually impossible, since the size of the microwave introduction window is determined by the wavelength of the microwaves. That is, in the plasma generating chamber, the microwaves are distributed in accordance with the intensity thereof, and the density distribution of the excited plasma is also dependent upon the distribution of the microwaves. Also, in this prior art dry etching apparatus, in order to define the spread of the excited plasma in the lateral direction to thereby make the density of the excited plasma uniform, a large electromagnet is provided to apply a magnetic field to the excited plasma, which is disadvantageous in size.
In another prior art dry etching apparatus, where two parallel plate electrodes are provided within a plasma generating chamber which also has mounted thereon a semiconductor substrate to be etched, the uniformity of density of excited plasma is controlled by the pressure thereof. Also in this type of dry etching apparatus, however, it is actually impossible to make the etching rate in a large size semiconductor substrate uniform. In order to effectively make the density of the excited plasma uniform, a plurality of holes are provided in a grounded electrode, and the number of the holes is controlled mechanically by a value mechanism to control all of the excited plasma supplied to the semiconductor substrate (see: JP-A-HEI1-165122). In this prior art dry etching apparatus, however, the flow of the excited plasma is not uniform, so that a time lag is required until the density of the excited plasma becomes stable, and also, it is disadvantageous to mechanically control the value mechanism.